I want to fill the remaining part of a CGCntext after drawing a rect? How can I do that? Thank you!
But the thing is, I set the blend mode of the cgcontext kCGBlendModeClear. I want to make the little rect in the context to transparent. If a draw the background first, can I still see the image in the rect?
If you want to fill the context (whose frame is bigRect), except for a rectangle inside it (whose frame is smallRect):
CGContextBeginPath(context);
CGContextAddRect(context, bigRect);
CGContextAddRect(context, smallRect);
CGContextSetFillColorWithColor(context, color);
CGContextEOFillPath(context, bigRect);
Do the background first...
CGRect bounds = [self bounds];
[[UIColor blackColor] set];
UIBezierPath* backgroundPath = [UIBezierPath bezierPathWithRect:bounds];
[backgroundPath fill];
CGRect innerRect = CGRectMake(self.bounds-10,
self.bounds-10,
self.bounds.width-20
self.bounds.height-20);
[[UIColor redColor] set];
UIBezierPath* foregroundPath = [UIBezierPath bezierPathWithRect:innerRect];
[foregroundPath fill];
Draw your background and then use CGContextClearRect to clear the area you want to be transparent.
arbitrary shape:
// do your foreground drawing
CGPathRef arbitraryShape; // asign your arbitrary shape
CGContextBeginPath(ctx);
CGContextAddRect(ctx, bounds); // rect in full size of the context
CGContextAddPath(ctx, arbitraryShape); // set the area you dont want to be drawn on
CGContextClip(ctx);
// do your background drawing
Related
I am looking for the way how to draw a hollow circle using Core Graphics (CGContext) in iOS. I tried to do it using the code:
- (void)drawRect:(CGRect)rect {
[super drawRect:rect];
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(ctx, 8.0);
CGContextSetStrokeColor(ctx, CGColorGetComponents([[UIColor redColor] CGColor]));
CGContextSetFillColor(ctx, CGColorGetComponents([[UIColor blueColor] CGColor]));
CGContextFillEllipseInRect(ctx, rect);
CGContextFillPath(ctx);
}
but it draws the filled circle.
Since this question is over discussed here but other examples like this give me only filled circles.
If you want to draw a circle within the rect, using Stroke methods and the rect in parameter you will draw a part of the cercle outside the rect.
You then have two choices, assuming you know the width of the circle you want to draw.
First, you can stroke the line, but you have to draw it in a smaller rect :
-(void)drawRect:(CGRect)rect {
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGFloat innerWidth = 8;
[[UIColor redColor] setStroke];
CGContextSetLineWidth(ctx, innerWidth);
// We add an ellipsis shifted by half the inner Width
CGContextAddEllipseInRect(ctx, CGRectInset(rect, innerWidth, innerWidth));
// Stroke the path
CGContextStrokePath(ctx);
}
You can also fill the circles using the even-odd rule (Apple docs)
-(void)drawRect:(CGRect)rect {
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGFloat innerWidth = 8;
[[UIColor redColor] setStroke];
// Add the outer circle
CGContextAddEllipseInRect(ctx, rect);
// Add the inner circle
CGContextAddEllipseInRect(ctx, CGRectInset(rect, innerWidth, innerWidth));
// Fill the path using the EO rule
CGContextEOFillPath(ctx);
}
If you only want the circle outline, don't fill it.
- (void)drawRect:(CGRect)rect {
[super drawRect:rect];
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(ctx, 8.0);
[[UIColor redColor] set];
CGContextStrokeEllipseInRect(ctx, rect);
}
Use CGContextStrokeEllipseInRect instead of CGContextFillEllipseInRect. And since you haven't built a path in the current context, get rid of CGContextFillPath.
One way you could do it is draw a filled circle and then draw a slightly smaller circle with CGContextSetBlendMode(UIGraphicsGetCurrentContext(),kCGBlendModeClear)
After your code add something like
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(ctx, 5.0);
CGContextSetBlendMode(ctx,kCGBlendModeClear)
CGContextSetFillColor(ctx, CGColorGetComponents([[UIColor blueColor] CGColor]));
CGContextFillEllipseInRect(ctx, rect);
CGContextFillPath(ctx);
UIGraphicsEndImageContext();
I use CGContextSetBlendMode(UIGraphicsGetCurrentContext(),kCGBlendModeClear) in my drawing application, which is probably a better use. Stroking the path will probably work for you.
I'm attempting to build a UIImage in code using CoreGraphics (via PaintCode) that has a border and a corner radius. I'm finding that the image has a noticeably thicker border around the corner. This seems like it would either be an iOS bug or something that I'm completely missing. Please advise.
Code:
CGRect rect = CGRectMake(0, 0, 53, 100);
//// UIGraphics for UIImage context
CGContextRef context = UIGraphicsGetCurrentContext();
UIGraphicsPushContext(context);
UIGraphicsBeginImageContextWithOptions(rect.size, NO, 0);
//// Rectangle Drawing
UIBezierPath *rectanglePath = [UIBezierPath bezierPathWithRoundedRect:rect cornerRadius:cornerRadius];
[backgroundColor setFill];
[rectanglePath fill];
[borderColor setStroke];
rectanglePath.lineWidth = 1.4;
[rectanglePath stroke];
//// UIBezierPath to Image
CGContextAddPath(context, rectanglePath.CGPath);
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsPopContext();
UIGraphicsEndImageContext();
return image;
Image:
Here's what a lineWidth of 1 and width of 60 looks like, it still seems a little thick:
For those of you following along at home:
Thanks to the helpful #PixelCutCompany I need to inset the bounds for the UIBezierPath so that the border doesn't exceed the frame of the image I am drawing.
Modified the code as follows for a lineWidth of 1.
CGRect boundedRectForRadius = CGRectMake(1, 1, 58, 98);
UIBezierPath *rectanglePath = [UIBezierPath bezierPathWithRoundedRect:boundedRectForRadius cornerRadius:cornerRadius];
Without this, it was cropping the image as so:
The problem also can be in shift real screen pixels coordinates.
Please check this discussion for more details:
Core Graphics is not drawing a line at the correct width
I have a UIView that draws different shapes. I can make a hole in my image to have it transparent, working fine, but the hole is only square,
//hole
CGRect holeRectValue = CGRectMake(300, 40, 80, 100);
CGRect holeRectIntersection = CGRectIntersection( holeRectValue, rect );
[[UIColor clearColor] setFill];
UIRectFill(holeRectIntersection);
Now I need to make the hole in the image but not as a rect, as the shape of my drawn figure,
Here is the code:
- (id)initWithFrame:(CGRect)frame forNode0:(CGPoint)node0 forNode1:(CGPoint)node1 fornode2:(CGPoint)node2 fornode3:(CGPoint)node3 fornode4:(CGPoint)node4 fornode5:(CGPoint)node5 fornode6:(CGPoint)node6 fornode7:(CGPoint)node7 fornode8:(CGPoint)node8 fornode9:(CGPoint)node9
{
self = [super initWithFrame:frame];
if (self) {
self.opaque = NO;
self.node0Pos = node0;
self.node1Pos = node1;
self.node2Pos = node2;
self.node3Pos = node3;
self.node4Pos = node4;
self.node5Pos = node5;
}
return self;
}
// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
- (void)drawRect:(CGRect)rect
{
//bgnd
UIGraphicsBeginImageContext(self.frame.size);
[[UIImage imageNamed:#"cat.jpeg"] drawInRect:self.bounds];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
[[UIColor colorWithPatternImage:image] setFill];
// Drawing code
UIRectFill(rect);
// Drawing code
//1. begin new path
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextBeginPath(context);
//2. move to initial starting point
CGContextMoveToPoint(context, self.node0Pos.x, self.node0Pos.y);
//3. add lines defining shape
CGContextAddLineToPoint(context, self.node1Pos.x, self.node1Pos.y);
CGContextAddLineToPoint(context, self.node2Pos.x, self.node2Pos.y);
CGContextAddLineToPoint(context, self.node3Pos.x, self.node3Pos.y);
CGContextAddLineToPoint(context, self.node4Pos.x, self.node4Pos.y);
CGContextAddLineToPoint(context, self.node5Pos.x, self.node5Pos.y);
//4. optionally close path
CGContextClosePath(context);
CGColorRef color;
//5. draw path
color = [UIColor colorWithRed:1 green:0 blue:228/255.0f alpha:0.5].CGColor;
//CGContextSetFillColor(context, color);
CGContextSetFillColorWithColor(context, color);
CGContextDrawPath(context, kCGPathFill);
//
//hole
CGRect holeRectValue = CGRectMake(300, 40, 80, 100);
CGRect holeRectIntersection = CGRectIntersection( holeRectValue, rect );
[[UIColor clearColor] setFill];
UIRectFill(holeRectIntersection);
}
So how do I make the "hole" with my actual context path?
P.S. I was doing some masking, but it leaves a white line around the hole, so I need to avoid this.
[[UIColor clearColor] setFill];
UIRectFill(holeRectIntersection);
This doesn’t do anything—drawing with a clear color is effectively a no-op. What you most likely want to do is add the rectangle you’re trying to cut out as part of the path you’re creating, i.e. inserting a call to CGContextAddRect before your CGContextClosePath. See Filling a Path in the Quartz 2D Programming Guide.
I believe what you're looking for is the CALayer.mask property. To create a "hole", you would generate a CALayer object with an alpha channel in the shape of the hole you want to make, and then apply it to the view you want to punch the hole in.
In semi-pseudocode:
CALayer *holeMask;
UIView *myView;
//
// Build the holeMask object via whatever means,
// and set myView to the target view that you want
// to punch the hole in...
//
myView.layer.mask = holeMask
I am drawing Circle using UIBezierPath. I want to draw it on CGLayer so that I can cache circle and draw text on it after some event(by calling setNeedsDisplay). How should I draw UIBezierPath on CGContextRef. My code below
- (void)drawRect:(CGRect)rect
{
// Drawing code
static CGLayerRef sTextLayer = NULL;
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGRect textBounds = CGRectMake(0, 0, 200, 100);
if (sTextLayer == NULL) {
sTextLayer = CGLayerCreateWithContext(ctx, textBounds.size, NULL);
CGContextRef textCtx = CGLayerGetContext(sTextLayer);
CGContextSetRGBFillColor (textCtx, 1.0, 0.0, 0.0, 1);
UIGraphicsPushContext(textCtx);
// Draw circle
UIBezierPath *circle = [UIBezierPath bezierPathWithOvalInRect:textBounds];
[[UIColor blackColor] setFill];
circle.lineWidth = 2.0;
[circle fill];
UIGraphicsPopContext();
}
if (self.drawString) {
UIFont *font = [UIFont systemFontOfSize:13.0];
NSString *string = #"HAPPY BIRTHDAY";
[string drawInRect:textBounds withFont:font];
}
}
Get the CGPath from the bezier path and then draw using CGContextAddPath and CGContextStrokePath. You may also want to use CGContextSetStrokeColorWithColor.
You can either:
Avoid the use of the CGLayerRef altogether and just have drawRect draw the UIBezierPath with fill method (or as Wain suggests, draw the circle using Core Graphics functions).
Add a CAShapeLayer, setting its path to the CGPathRef of the UIBezierPath, and then add the text as a CATextLayer or a UILabel subview (in which case, you don't need a drawRect implementation at all).
I infer that you're worried about the efficiency of redrawing the circle, but when you render the text, it probably needs to re-render the circle anyway. You could always save a reference to the UIBezierPath or do a snapshot, but I'm not sure that's worth it. You can benchmark it and see.
I might not be explaining this in the best way possible, so please bear with me.
What I have is a drawn CGPath on top of a MKMapView object:
The way I was able to achieve this is to create a CGPath for the darker blue line, then create a copy of that path, and then stroke a thicker version of it with a semi-transparent blue color. Here's the code that I'm currently using for this:
// set the shadow around the path line
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSaveGState(context);
CGContextSetRGBStrokeColor(context, 0.0f, 0.0f, 0.0f, 0.0f);
CGContextSetRGBFillColor(context, 0.0f, 0.0f, 1.0f, 0.4f);
CGPathRef shadowPath = CGPathCreateCopyByStrokingPath(self.path.CGPath, NULL, 80.0f, kCGLineCapRound, kCGLineJoinRound, 0.0f);
CGContextBeginPath(context);
CGContextAddPath(context, shadowPath);
CGContextDrawPath(context, kCGPathFillStroke);
CGContextRestoreGState(context);
CGPathRelease(shadowPath);
Works pretty well, nothing wrong so far.
However, what I would like to do though is to get a CGPathRef of the outline of that thicker semi-transparent blue area. Here's another screenshot showing the pseudo-path that I want out of this (hand drawn in red):
How is this possible?
Simple: just use CGPathCreateCopyByStrokingPath. Pass in a wide line width, and a cap of kCGLineCapRound.
You can draw two stokes.
one stroke with width n (which n is the outline width) and black color.
another stroke is then drawn on top of the first one, with eraser mode:
CGContextSetBlendMode(context, kCGBlendModeCopy);
CGContextSetFillColorWithColor(context, [[UIColor clearColor] CGColor]);